package com.coderising.array;

public class ArrayUtil {

    /**
     * 给定一个整形数组a , 对该数组的值进行置换
     * 例如： a = [7, 9 , 30, 3]  ,   置换后为 [3, 30, 9,7]
     * 如果     a = [7, 9, 30, 3, 4] , 置换后为 [4,3, 30 , 9,7]
     *
     * @param origin
     * @return
     */
    public void reverseArray(int[] origin) {
        int i = 0;
        while (i < origin.length - 1 - i) {
            int temp = origin[origin.length - 1 - i];
            origin[origin.length - 1 - i] = origin[i];
            origin[i] = temp;
            i++;
        }
    }

    /**
     * 现在有如下的一个数组：   int oldArr[]={1,3,4,5,0,0,6,6,0,5,4,7,6,7,0,5}
     * 要求将以上数组中值为0的项去掉，将不为0的值存入一个新的数组，生成的新数组为：
     * {1,3,4,5,6,6,5,4,7,6,7,5}
     *
     * @param oldArray
     * @return
     */

    public int[] removeZero(int[] oldArray) {
        int point = 0;
        for (int i : oldArray) {
            if (i != 0) {
                oldArray[point++] = i;
            }
        }
        int[] newArray = new int[point];
        System.arraycopy(oldArray, 0, newArray, 0, point);
        return newArray;
    }

    /**
     * 给定两个已经排序好的整形数组， a1和a2 ,  创建一个新的数组a3, 使得a3 包含a1和a2 的所有元素， 并且仍然是有序的
     * 例如 a1 = [3, 5, 7,8]   a2 = [4, 5, 6,7]    则 a3 为[3,4,5,6,7,8]    , 注意： 已经消除了重复
     *
     * @param array1
     * @param array2
     * @return
     */

    public int[] merge(int[] array1, int[] array2) {
        //两个指针
        int pos1 = 0;
        int pos2 = 0;
        int point = 0;
        int[] newArray = new int[array1.length + array2.length];
        while (pos1 < array1.length && pos2 < array2.length) {
            if (array1[pos1] > array2[pos2]) {
                newArray[point++] = array2[pos2++];
            } else if (array1[pos1] < array2[pos2]) {
                newArray[point++] = array1[pos1++];
            } else {
                newArray[point++] = array1[pos1++];
                pos2++;
            }
        }
        while (pos1 < array1.length) {
            newArray[point++] = array1[pos1++];
        }
        while (pos1 < array2.length) {
            newArray[point++] = array1[pos2++];
        }
        int[] array = new int[point];
        System.arraycopy(newArray, 0, array, 0, point);
        return array;
    }

    /**
     * 把一个已经存满数据的数组 oldArray的容量进行扩展， 扩展后的新数据大小为oldArray.length + size
     * 注意，老数组的元素在新数组中需要保持
     * 例如 oldArray = [2,3,6] , size = 3,则返回的新数组为
     * [2,3,6,0,0,0]
     *
     * @param oldArray
     * @param size
     * @return
     */
    public int[] grow(int[] oldArray, int size) {
        int[] newArray = new int[oldArray.length + size];
        System.arraycopy(oldArray, 0, newArray, 0, oldArray.length);
        return newArray;
    }

    /**
     * 斐波那契数列为：1，1，2，3，5，8，13，21......  ，给定一个最大值， 返回小于该值的数列
     * 例如， max = 15 , 则返回的数组应该为 [1，1，2，3，5，8，13]
     * max = 1, 则返回空数组 []
     *
     * @param max
     * @return
     */
    public int[] fibonacci(int max) {
        int a = 0;
        int b = 1;
        int[] array = new int[max];
        int i = 0;
        if (max >= 2) {
            array[i++] = 1;
        }
        while (a + b < max) {
            int temp = b;
            b = a + b;
            a = temp;
            array[i++] = b;
        }
        int[] newArray = new int[i];
        System.arraycopy(array, 0, newArray, 0, i);
        return newArray;
    }

    /**
     * 返回小于给定最大值max的所有素数数组
     * 例如max = 23, 返回的数组为[2,3,5,7,11,13,17,19]
     *
     * @param max
     * @return
     */
    public int[] getPrimes(int max) {
        int[] array = new int[max / 2 + 1];
        int pos = 0;
        for (int i = 1; i < max; i++) {
            if (prime(i)) {
                array[pos++] = i;
            }
        }
        int[] newArray = new int[pos];
        System.arraycopy(array, 0, newArray, 0, pos);
        return newArray;
    }

    private boolean prime(int value) {
        if (value < 2) {
            return false;
        } else if (value == 2) {
            return true;
        } else {
            for (int i = 2; i < value / 2 + 1; i++) {
                if (value % 2 == 0) {
                    return false;
                }
            }
            return true;
        }
    }

    /**
     * 所谓“完数”， 是指这个数恰好等于它的因子之和，例如6=1+2+3
     * 给定一个最大值max， 返回一个数组， 数组中是小于max 的所有完数
     *
     * @param max
     * @return
     */
    public int[] getPerfectNumbers(int max) {
        int pos = 0;
        int[] array = new int[max];
        for (int i = 1; i < max; i++) {
            if (perfectNumber(i)) {
                array[pos++] = i;
            }
        }
        int[] newArray = new int[pos];
        System.arraycopy(array, 0, newArray, 0, pos);
        return newArray;
    }

    private boolean perfectNumber(int value) {
        if (value == 1 || prime(value)) {
            return false;
        } else {
            int sum = 0;
            for (int i = 1; i <= value / 2; i++) {
                if (value % i == 0) {
                    sum += i;
                }
            }
            if (sum == value) {
                return true;
            }
            return false;
        }
    }

    /**
     * 用seperator 把数组 array给连接起来
     * 例如array= [3,8,9], seperator = "-"
     * 则返回值为"3-8-9"
     *
     * @param array
     * @param seperator
     * @return
     */
    public String join(int[] array, String seperator) {
        String out = "";
        for (int i = 0; i < array.length; i++) {
            if (i == 0) {
                out += String.valueOf(i);
            } else {
                out += seperator + String.valueOf(i);
            }
        }
        return out;
    }


    public static void main(String[] args) {
        ArrayUtil arrayUtil = new ArrayUtil();
        //reverse
        int[] a = {7, 9, 30, 3};
        arrayUtil.reverseArray(a);
        System.out.println(a);

        //remove zero
        int[] zero = {1, 3, 4, 5, 0, 0, 6, 6, 0, 5, 4, 7, 6, 7, 0, 5};
        int[] afterZero = arrayUtil.removeZero(zero);
        System.out.println(afterZero);

        //merge
        int[] a1 = {3, 5, 7, 8};
        int[] a2 = {4, 5, 6, 7};
        int[] merge = arrayUtil.merge(a1, a2);
        System.out.println(merge);

        //grow
        int[] oldArray = {2, 3, 6};
        int[] grow = arrayUtil.grow(oldArray, 3);
        System.out.println(grow);

        //fibonacci
        int[] fibonacci = arrayUtil.fibonacci(2);
        System.out.println(fibonacci);

        //primes
        int[] primes = arrayUtil.getPrimes(15);
        System.out.println(primes);

        //perfect
        int[] perfect = arrayUtil.getPerfectNumbers(500);
        System.out.println(perfect);

        //join
        int[] joinArray = {2};
        String join = arrayUtil.join(joinArray, "-");
        System.out.println(join);

    }
}
